Xdm manages
a collection of X displays, which may be on the local host or remote servers.
The design of xdm was guided by the needs of X terminals as well as The
Open Group standard XDMCP, the X Display Manager Control Protocol. Xdm provides
services similar to those provided by init, getty and login on character
terminals: prompting for login name and password, authenticating the user,
and running a ``session.''

A ``session'' is defined by the lifetime of a particular
process; in the traditional character-based terminal world, it is the user's
login shell. In the xdm context, it is an arbitrary session manager. This
is because in a windowing environment, a user's login shell process does
not necessarily have any terminal-like interface with which to connect. When
a real session manager is not available, a window manager or terminal emulator
is typically used as the ``session manager,'' meaning that termination of this
process terminates the user's session.

When the session is terminated, xdm
resets the X server and (optionally) restarts the whole process.

When xdm
receives an Indirect query via XDMCP, it can run a chooser process to perform
an XDMCP BroadcastQuery (or an XDMCP Query to specified hosts) on behalf
of the display and offer a menu of possible hosts that offer XDMCP display
management. This feature is useful with X terminals that do not offer a
host menu themselves.

Xdm can be configured to ignore BroadcastQuery messages
from selected hosts. This is useful when you don't want the host to appear
in menus produced by chooser or X terminals themselves.

Because xdm provides
the first interface that users will see, it is designed to be simple to
use and easy to customize to the needs of a particular site. Xdm has many
options, most of which have reasonable defaults. Browse through the various
sections of this manual, picking and choosing the things you want to change.
Pay particular attention to the Session Program section, which will describe
how to set up the style of session desired.

xdm is highly configurable,
and most of its behavior can be controlled by resource files and shell
scripts. The names of these files themselves are resources read from the
file xdm-config or the file named by the -config option.

xdm offers display
management two different ways. It can manage X servers running on the local
machine and specified in Xservers, and it can manage remote X servers (typically
X terminals) using XDMCP (the XDM Control Protocol) as specified in the
Xaccess file.

The resources of the X clients run by xdm outside the user's
session, including xdm's own login window, can be affected by setting resources
in the Xresources file.

For X terminals that do not offer a menu of hosts
to get display management from, xdm can collect willing hosts and run the
chooser program to offer the user a menu. For X displays attached to a host,
this step is typically not used, as the local host does the display management.

After resetting the X server, xdm runs the Xsetup script to assist in setting
up the screen the user sees along with the xlogin widget.

The xlogin widget,
which xdm presents, offers the familiar login and password prompts.

After
the user logs in, xdm runs the Xstartup script as root.

Then xdm runs the
Xsession script as the user. This system session file may do some additional
startup and typically runs the .xsession script in the user's home directory.
When the Xsession script exits, the session is over.

At the end of the session,
the Xreset script is run to clean up, the X server is reset, and the cycle
starts over.

The file __projectroot__/lib/X11/xdm/xdm-errors will contain
error messages from xdm and anything output to stderr by Xsetup, Xstartup,
Xsession or Xreset. When you have trouble getting xdm working, check this
file to see if xdm has any clues to the trouble.

All of these options,
except -config itself, specify values that can also be specified in the
configuration file as resources.

-configconfiguration_file

Names the configuration
file, which specifies resources to control the behavior of xdm./usr/X11R6/lib/X11/xdm/xdm-config
is the default. See the section Configuration File.

-nodaemon

Specifies ``false''
as the value for the DisplayManager.daemonMode resource. This suppresses
the normal daemon behavior, which is for xdm to close all file descriptors,
disassociate itself from the controlling terminal, and put itself in the
background when it first starts up.

-debugdebug_level

Specifies the numeric
value for the DisplayManager.debugLevel resource. A non-zero value causes
xdm to print lots of debugging statements to the terminal; it also disables
the DisplayManager.daemonMode resource, forcing xdm to run synchronously.
To interpret these debugging messages, a copy of the source code for xdm
is almost a necessity. No attempt has been made to rationalize or standardize
the output.

-errorerror_log_file

Specifies the value for the DisplayManager.errorLogFile
resource. This file contains errors from xdm as well as anything written
to stderr by the various scripts and programs run during the progress of
the session.

-resourcesresource_file

Specifies the value for the DisplayManager*resources
resource. This file is loaded using xrdb to specify configuration parameters
for the authentication widget.

-serverserver_entry

Specifies the value for
the DisplayManager.servers resource. See the section Local Server Specification
for a description of this resource.

-udpPortport_number

Specifies the value
for the DisplayManager.requestPort resource. This sets the port-number which
xdm will monitor for XDMCP requests. As XDMCP uses the registered well-known
UDP port 177, this resource should not be changed except for debugging.
If set to 0 xdm will not listen for XDMCP or Chooser requests.

-sessionsession_program

Specifies
the value for the DisplayManager*session resource. This indicates the program
to run as the session after the user has logged in.

-xrmresource_specification

Allows
an arbitrary resource to be specified, as in most X Toolkit applications.

At many stages the actions of xdm can be controlled through the
use of its configuration file, which is in the X resource format. Some resources
modify the behavior of xdm on all displays, while others modify its behavior
on a single display. Where actions relate to a specific display, the display
name is inserted into the resource name between ``DisplayManager'' and the
final resource name segment.

For local displays, the resource name and class
are as read from the Xservers file.

For remote displays, the resource name
is what the network address of the display resolves to. See the removeDomain
resource. The name must match exactly; xdm is not aware of all the network
aliases that might reach a given display. If the name resolve fails, the
address is used. The resource class is as sent by the display in the XDMCP
Manage request.

Because the resource manager uses colons to separate the
name of the resource from its value and dots to separate resource name
parts, xdm substitutes underscores for both dots and colons when generating
the resource name. For example, DisplayManager.expo_x_org_0.startup is the
name of the resource which defines the startup shell file for the ``expo.x.org:0''
display.

DisplayManager.servers

This resource either specifies a file name
full of server entries, one per line (if the value starts with a slash),
or a single server entry. See the section Local Server Specification for
the details.

DisplayManager.requestPort

This indicates the UDP port number
which xdm uses to listen for incoming XDMCP requests. Unless you need to
debug the system, leave this with its default value of 177.

DisplayManager.errorLogFile

Error
output is normally directed at the system console. To redirect it, set
this resource to a file name. A method to send these messages to syslog
should be developed for systems which support it; however, the wide variety
of interfaces precludes any system-independent implementation. This file
also contains any output directed to stderr by the Xsetup, Xstartup, Xsession
and Xreset files, so it will contain descriptions of problems in those
scripts as well.

DisplayManager.debugLevel

If the integer value of this resource
is greater than zero, reams of debugging information will be printed. It
also disables daemon mode, which would redirect the information into the
bit-bucket, and allows non-root users to run xdm, which would normally not
be useful.

DisplayManager.daemonMode

Normally, xdm attempts to make itself
into a daemon process unassociated with any terminal. This is accomplished
by forking and leaving the parent process to exit, then closing file descriptors
and releasing the controlling terminal. In some environments this is not
desired (in particular, when debugging). Setting this resource to ``false''
will disable this feature.

DisplayManager.pidFile

The filename specified will
be created to contain an ASCII representation of the process-id of the main
xdm process. Xdm also uses file locking on this file to attempt to eliminate
multiple daemons running on the same machine, which would cause quite a
bit of havoc.

DisplayManager.lockPidFile

This is the resource which controls
whether xdm uses file locking to keep multiple display managers from running
amok. On System V, this uses the lockf library call, while on BSD it uses
flock.

DisplayManager.authDir

This names a directory under which xdm stores
authorization files while initializing the session. The default value is
__projectroot__/lib/X11/xdm. Can be overridden for specific displays by
DisplayManager.DISPLAY.authFile.

DisplayManager.autoRescan

This boolean controls
whether xdm rescans the configuration, servers, access control and authentication
keys files after a session terminates and the files have changed. By default
it is ``true.'' You can force xdm to reread these files by sending a SIGHUP
to the main process.

DisplayManager.removeDomainname

When computing the display
name for XDMCP clients, the name resolver will typically create a fully
qualified host name for the terminal. As this is sometimes confusing, xdm
will remove the domain name portion of the host name if it is the same
as the domain name of the local host when this variable is set. By default
the value is ``true.''

DisplayManager.keyFile

XDM-AUTHENTICATION-1 style XDMCP authentication
requires that a private key be shared between xdm and the terminal. This
resource specifies the file containing those values. Each entry in the
file consists of a display name and the shared key. By default, xdm does
not include support for XDM-AUTHENTICATION-1, as it requires DES which is
not generally distributable because of United States export restrictions.

DisplayManager.accessFile

To prevent unauthorized XDMCP service and to allow
forwarding of XDMCP IndirectQuery requests, this file contains a database
of hostnames which are either allowed direct access to this machine, or
have a list of hosts to which queries should be forwarded to. The format
of this file is described in the section XDMCP Access Control.

DisplayManager.exportList

A
list of additional environment variables, separated by white space, to
pass on to the Xsetup, Xstartup, Xsession, and Xreset programs.

DisplayManager.randomFile

A
file to checksum to generate the seed of authorization keys. This should
be a file that changes frequently. The default is /dev/mem.

DisplayManager.greeterLib

On
systems that support a dynamically-loadable greeter library, the name of
the library. The default is __projectroot__/lib/X11/xdm/libXdmGreet.so.

DisplayManager.choiceTimeout

Number
of seconds to wait for display to respond after user has selected a host
from the chooser. If the display sends an XDMCP IndirectQuery within this
time, the request is forwarded to the chosen host. Otherwise, it is assumed
to be from a new session and the chooser is offered again. Default is 15.

DisplayManager.sourceAddress

Use the numeric IP address of the incoming connection
on multihomed hosts instead of the host name. This is to avoid trying to
connect on the wrong interface which might be down at this time.

DisplayManager.willing

This
specifies a program which is run (as) root when an an XDMCP BroadcastQuery
is received and this host is configured to offer XDMCP display management.
The output of this program may be displayed on a chooser window. If no
program is specified, the string Willing to manage is sent.

DisplayManager.DISPLAY.resources

This
resource specifies the name of the file to be loaded by xrdb as the resource
database onto the root window of screen 0 of the display. The Xsetup program,
the Login widget, and chooser will use the resources set in this file. This
resource data base is loaded just before the authentication procedure is
started, so it can control the appearance of the login window. See the
section Authentication Widget, which describes the various resources that
are appropriate to place in this file. There is no default value for this
resource, but __projectroot__/lib/X11/xdm/Xresources is the conventional
name.

DisplayManager.DISPLAY.chooser

Specifies the program run to offer a host
menu for Indirect queries redirected to the special host name CHOOSER. __projectroot__/lib/X11/xdm/chooser
is the default. See the sections XDMCP Access Control and Chooser.

DisplayManager.DISPLAY.xrdb

Specifies
the program used to load the resources. By default, xdm uses __projectroot__/bin/xrdb.

DisplayManager.DISPLAY.cpp

This specifies the name of the C preprocessor which
is used by xrdb.

DisplayManager.DISPLAY.setup

This specifies a program which
is run (as root) before offering the Login window. This may be used to
change the appearance of the screen around the Login window or to put up
other windows (e.g., you may want to run xconsole here). By default, no program
is run. The conventional name for a file used here is Xsetup. See the section
Setup Program.

DisplayManager.DISPLAY.startup

This specifies a program which
is run (as root) after the authentication process succeeds. By default,
no program is run. The conventional name for a file used here is Xstartup.
See the section Startup Program.

DisplayManager.DISPLAY.session

This specifies
the session to be executed (not running as root). By default, __projectroot__/bin/xterm
is run. The conventional name is Xsession. See the section Session Program.

DisplayManager.DISPLAY.reset

This specifies a program which is run (as root)
after the session terminates. By default, no program is run. The conventional
name is Xreset. See the section Reset Program.

DisplayManager.DISPLAY.openDelay

DisplayManager.DISPLAY.openRepeat

DisplayManager.DISPLAY.openTimeout

DisplayManager.DISPLAY.startAttempts

These
numeric resources control the behavior of xdm when attempting to open intransigent
servers. openDelay is the length of the pause (in seconds) between successive
attempts, openRepeat is the number of attempts to make, openTimeout is
the amount of time to wait while actually attempting the open (i.e., the
maximum time spent in the connect(2)
system call) and startAttempts is
the number of times this entire process is done before giving up on the
server. After openRepeat attempts have been made, or if openTimeout seconds
elapse in any particular attempt, xdm terminates and restarts the server,
attempting to connect again. This process is repeated startAttempts times,
at which point the display is declared dead and disabled. Although this
behavior may seem arbitrary, it has been empirically developed and works
quite well on most systems. The default values are 5 for openDelay, 5 for
openRepeat, 30 for openTimeout and 4 for startAttempts.

DisplayManager.DISPLAY.pingInterval

DisplayManager.DISPLAY.pingTimeout

To
discover when remote displays disappear, xdm occasionally pings them, using
an X connection and XSync calls. pingInterval specifies the time (in minutes)
between each ping attempt, pingTimeout specifies the maximum amount of
time (in minutes) to wait for the terminal to respond to the request. If
the terminal does not respond, the session is declared dead and terminated.
By default, both are set to 5 minutes. If you frequently use X terminals
which can become isolated from the managing host, you may wish to increase
this value. The only worry is that sessions will continue to exist after
the terminal has been accidentally disabled. xdm will not ping local displays.
Although it would seem harmless, it is unpleasant when the workstation
session is terminated as a result of the server hanging for NFS service
and not responding to the ping.

DisplayManager.DISPLAY.terminateServer

This
boolean resource specifies whether the X server should be terminated when
a session terminates (instead of resetting it). This option can be used
when the server tends to grow without bound over time, in order to limit
the amount of time the server is run. The default value is ``false.''

DisplayManager.DISPLAY.userPath

Xdm
sets the PATH environment variable for the session to this value. It should
be a colon separated list of directories; see sh(1)
for a full description.
``:/bin:/usr/bin:/usr/X11R6/bin:/usr/ucb'' is a common setting. The default
value can be specified at build time in the X system configuration file
with DefaultUserPath.

DisplayManager.DISPLAY.systemPath

Xdm sets the PATH environment
variable for the startup and reset scripts to the value of this resource.
The default for this resource is specified at build time by the DefaultSystemPath
entry in the system configuration file; ``/etc:/bin:/usr/bin:/usr/X11R6/bin:/usr/ucb''
is a common choice. Note the absence of ``.'' from this entry. This is a good
practice to follow for root; it avoids many common Trojan Horse system
penetration schemes.

DisplayManager.DISPLAY.systemShell

Xdm sets the SHELL
environment variable for the startup and reset scripts to the value of
this resource. It is /bin/sh by default.

DisplayManager.DISPLAY.failsafeClient

If
the default session fails to execute, xdm will fall back to this program.
This program is executed with no arguments, but executes using the same
environment variables as the session would have had (see the section Session
Program). By default, __projectroot__/bin/xterm is used.

DisplayManager.DISPLAY.grabServer

DisplayManager.DISPLAY.grabTimeout

To
improve security, xdm grabs the server and keyboard while reading the login
name and password. The grabServer resource specifies if the server should
be held for the duration of the name/password reading. When ``false,'' the
server is ungrabbed after the keyboard grab succeeds, otherwise the server
is grabbed until just before the session begins. The default is ``false.'' The
grabTimeout resource specifies the maximum time xdm will wait for the grab
to succeed. The grab may fail if some other client has the server grabbed,
or possibly if the network latencies are very high. This resource has a
default value of 3 seconds; you should be cautious when raising it, as
a user can be spoofed by a look-alike window on the display. If the grab
fails, xdm kills and restarts the server (if possible) and the session.

DisplayManager.DISPLAY.authorize

DisplayManager.DISPLAY.authName

authorize is
a boolean resource which controls whether xdm generates and uses authorization
for the local server connections. If authorization is used, authName is
a list of authorization mechanisms to use, separated by white space. XDMCP
connections dynamically specify which authorization mechanisms are supported,
so authName is ignored in this case. When authorize is set for a display
and authorization is not available, the user is informed by having a different
message displayed in the login widget. By default, authorize is ``true.'' authName
is ``MIT-MAGIC-COOKIE-1,'' or, if XDM-AUTHORIZATION-1 is available, ``XDM-AUTHORIZATION-1
MIT-MAGIC-COOKIE-1.''

DisplayManager.DISPLAY.authFile

This file is used to communicate
the authorization data from xdm to the server, using the -auth server command
line option. It should be kept in a directory which is not world-writable
as it could easily be removed, disabling the authorization mechanism in
the server. If not specified, a name is generated from DisplayManager.authDir
and the name of the display.

DisplayManager.DISPLAY.authComplain

If set to
``false,'' disables the use of the unsecureGreeting in the login window. See
the section Authentication Widget. The default is ``true.''

DisplayManager.DISPLAY.resetSignal

The
number of the signal xdm sends to reset the server. See the section Controlling
the Server. The default is 1 (SIGHUP).

DisplayManager.DISPLAY.termSignal

The
number of the signal xdm sends to terminate the server. See the section
Controlling the Server. The default is 15 (SIGTERM).

DisplayManager.DISPLAY.resetForAuth

The
original implementation of authorization in the sample server reread the
authorization file at server reset time, instead of when checking the initial
connection. As xdm generates the authorization information just before
connecting to the display, an old server would not get up-to-date authorization
information. This resource causes xdm to send SIGHUP to the server after
setting up the file, causing an additional server reset to occur, during
which time the new authorization information will be read. The default is
``false,'' which will work for all MIT servers.

DisplayManager.DISPLAY.userAuthDir

When
xdm is unable to write to the usual user authorization file ($HOME/.Xauthority),
it creates a unique file name in this directory and points the environment
variable XAUTHORITY at the created file. It uses /tmp by default.

Note that this file mostly contains references to other files. Note also
that some of the resources are specified with ``*'' separating the components.
These resources can be made unique for each different display, by replacing
the ``*'' with the display-name, but normally this is not very useful. See the
Resources section for a complete discussion.

The database
file specified by the DisplayManager.accessFile provides information which
xdm uses to control access from displays requesting XDMCP service. This
file contains three types of entries: entries which control the response
to Direct and Broadcast queries, entries which control the response to
Indirect queries, and macro definitions.

The format of the Direct entries
is simple, either a host name or a pattern, which is distinguished from
a host name by the inclusion of one or more meta characters (`*' matches
any sequence of 0 or more characters, and `?' matches any single character)
which are compared against the host name of the display device. If the entry
is a host name, all comparisons are done using network addresses, so any
name which converts to the correct network address may be used. For patterns,
only canonical host names are used in the comparison, so ensure that you
do not attempt to match aliases. Preceding either a host name or a pattern
with a `!' character causes hosts which match that entry to be excluded.

To
only respond to Direct queries for a host or pattern, it can be followed
by the optional ``NOBROADCAST'' keyword. This can be used to prevent an xdm
server from appearing on menus based on Broadcast queries.

An Indirect entry
also contains a host name or pattern, but follows it with a list of host
names or macros to which indirect queries should be sent.

A macro definition
contains a macro name and a list of host names and other macros that the
macro expands to. To distinguish macros from hostnames, macro names start
with a `%' character. Macros may be nested.

Indirect entries may also specify
to have xdm run chooser to offer a menu of hosts to connect to. See the
section Chooser.

When checking access for a particular display host, each
entry is scanned in turn and the first matching entry determines the response.
Direct and Broadcast entries are ignored when scanning for an Indirect
entry and vice-versa.

Blank lines are ignored, `#' is treated as a comment
delimiter causing the rest of that line to be ignored, and `\newline' causes
the newline to be ignored, allowing indirect host lists to span multiple
lines.

For X terminals that do not offer a host menu for use with Broadcast
or Indirect queries, the chooser program can do this for them. In the Xaccess
file, specify ``CHOOSER'' as the first entry in the Indirect host list. Chooser
will send a Query request to each of the remaining host names in the list
and offer a menu of all the hosts that respond.

The list may consist of
the word ``BROADCAST,'' in which case chooser will send a Broadcast instead,
again offering a menu of all hosts that respond. Note that on some operating
systems, UDP packets cannot be broadcast, so this feature will not work.

Example Xaccess file using chooser:

extract.lcs.mit.edu CHOOSER %HOSTS #offer a menu of these hosts
xtra.lcs.mit.edu CHOOSER BROADCAST #offer a menu of all hosts

The program to use for chooser is specified by the DisplayManager.DISPLAY.chooser
resource. For more flexibility at this step, the chooser could be a shell
script. Chooser is the session manager here; it is run instead of a child
xdm to manage the display.

Resources for this program can be put into the
file named by DisplayManager.DISPLAY.resources.

When the user selects a host,
chooser prints the host chosen, which is read by the parent xdm, and exits.
xdm closes its connection to the X server, and the server resets and sends
another Indirect XDMCP request. xdm remembers the user's choice (for DisplayManager.choiceTimeout
seconds) and forwards the request to the chosen host, which starts a session
on that display.

The resource DisplayManager.servers
gives a server specification or, if the values starts with a slash (/),
the name of a file containing server specifications, one per line.

Each
specification indicates a display which should constantly be managed and
which is not using XDMCP. This method is used typically for local servers
only. If the resource or the file named by the resource is empty, xdm will
offer XDMCP service only.

Each specification consists of at least three
parts: a display name, a display class, a display type, and (for local
servers) a command line to start the server. A typical entry for local
display number 0 would be:

:0 Digital-QV local /usr/X11R6/bin/X :0

The display types are:

local local display: xdm must run the server
foreign remote display: xdm opens an X connection to a running server

The display name must be something that can be passed in the -display option
to an X program. This string is used to generate the display-specific resource
names, so be careful to match the names (e.g., use ``:0 Sun-CG3 local /usr/X11R6/bin/X
:0'' instead of ``localhost:0 Sun-CG3 local /usr/X11R6/bin/X :0'' if your other
resources are specified as ``DisplayManager._0.session''). The display class
portion is also used in the display-specific resources, as the class of
the resource. This is useful if you have a large collection of similar
displays (such as a corral of X terminals) and would like to set resources
for groups of them. When using XDMCP, the display is required to specify
the display class, so the manual for your particular X terminal should
document the display class string for your device. If it doesn't, you can
run xdm in debug mode and look at the resource strings which it generates
for that device, which will include the class string.

When xdm starts a
session, it sets up authorization data for the server. For local servers,
xdm passes ``-authfilename'' on the server's command line to point it at its
authorization data. For XDMCP servers, xdm passes the authorization data
to the server via the Accept XDMCP request.

Please note the translations entry; it specifies a few new translations
for the widget which allow users to escape from the default session (and
avoid troubles that may occur in it). Note that if #override is not specified,
the default translations are removed and replaced by the new value, not
a very useful result as some of the default translations are quite useful
(such as ``<Key>: insert-char ()'' which responds to normal typing).

This file
may also contain resources for the setup program and chooser.

The
Xsetup file is run after the server is reset, but before the Login window
is offered. The file is typically a shell script. It is run as root, so should
be careful about security. This is the place to change the root background
or bring up other windows that should appear on the screen along with the
Login widget.

In addition to any specified by DisplayManager.exportList,
the following environment variables are passed:

DISPLAY the associated display name
PATH the value of DisplayManager.DISPLAY.systemPath SHELL the value of DisplayManager.DISPLAY.systemShell XAUTHORITY may be set to an authority file

Note that since xdm grabs the keyboard, any other windows will not be able
to receive keyboard input. They will be able to interact with the mouse,
however; beware of potential security holes here. If DisplayManager.DISPLAY.grabServer
is set, Xsetup will not be able to connect to the display at all. Resources
for this program can be put into the file named by DisplayManager.DISPLAY.resources.

The authentication widget reads a name/password pair
from the keyboard. Nearly every imaginable parameter can be controlled
with a resource. Resources for this widget should be put into the file
named by DisplayManager.DISPLAY.resources. All of these have reasonable default
values, so it is not necessary to specify any of them.

The geometry of the Login
widget is normally computed automatically. If you wish to position it elsewhere,
specify each of these resources.

xlogin.Login.foreground

The color used to
display the typed-in user name.

xlogin.Login.font

The font used to display the
typed-in user name.

xlogin.Login.greeting

A string which identifies this window.
The default is ``X Window System.''

xlogin.Login.unsecureGreeting

When X authorization
is requested in the configuration file for this display and none is in
use, this greeting replaces the standard greeting. The default is ``This
is an unsecure session''

xlogin.Login.greetFont

The font used to display the
greeting.

xlogin.Login.greetColor

The color used to display the greeting.

xlogin.Login.namePrompt

The
string displayed to prompt for a user name. Xrdb strips trailing white space
from resource values, so to add spaces at the end of the prompt (usually
a nice thing), add spaces escaped with backslashes. The default is ``Login:
''

xlogin.Login.passwdPrompt

The string displayed to prompt for a password.
The default is ``Password: ''

xlogin.Login.promptFont

The font used to display
both prompts.

xlogin.Login.promptColor

The color used to display both prompts.

xlogin.Login.fail

A message which is displayed when the authentication fails.
The default is ``Login incorrect''

xlogin.Login.failFont

The font used to display
the failure message.

xlogin.Login.failColor

The color used to display the failure
message.

xlogin.Login.failTimeout

The number of seconds that the failure message
is displayed. The default is 30.

xlogin.Login.translations

This specifies the
translations used for the login widget. Refer to the X Toolkit documentation
for a complete discussion on translations. The default translation table
is:

If set to ``false'', don't allow root (and any other
user with uid = 0) to log in directly. The default is ``true''.

xlogin.Login.allowNullPasswd

If
set to ``true'', allow an otherwise failing password match to succeed if the
account does not require a password at all. The default is ``false'', so only
users that have passwords assigned can log in.

The actions which are supported
by the widget are:

delete-previous-character

Erases the character before the
cursor.

delete-character

Erases the character after the cursor.

move-backward-character

Moves
the cursor backward.

move-forward-character

Moves the cursor forward.

move-to-begining

(Apologies
about the spelling error.) Moves the cursor to the beginning of the editable
text.

move-to-end

Moves the cursor to the end of the editable text.

erase-to-end-of-line

Erases
all text after the cursor.

erase-line

Erases the entire text.

finish-field

If
the cursor is in the name field, proceeds to the password field; if the
cursor is in the password field, checks the current name/password pair.
If the name/password pair is valid, xdm starts the session. Otherwise
the failure message is displayed and the user is prompted again.

abort-session

Terminates
and restarts the server.

abort-display

Terminates the server, disabling it.
This action is not accessible in the default configuration. There are various
reasons to stop xdm on a system console, such as when shutting the system
down, when using xdmshell, to start another type of server, or to generally
access the console. Sending xdm a SIGHUP will restart the display. See the
section Controlling XDM.

restart-session

Resets the X server and starts a
new session. This can be used when the resources have been changed and
you want to test them or when the screen has been overwritten with system
messages.

insert-char

Inserts the character typed.

set-session-argument

Specifies
a single word argument which is passed to the session at startup. See the
section Session Program.

allow-all-access

Disables access control in the server.
This can be used when the .Xauthority file cannot be created by xdm. Be
very careful using this; it might be better to disconnect the machine from
the network before doing this.

On some systems (OpenBSD) the user's shell
must be listed in /etc/shells to allow login through xdm. The normal password
and account expiration dates are enforced too.

The Xstartup
program is run as root when the user logs in. It is typically a shell script.
Since it is run as root, Xstartup should be very careful about security.
This is the place to put commands which add entries to /etc/utmp (the
sessreg program may be useful here), mount users' home directories from
file servers, or abort the session if logins are not allowed.

In addition
to any specified by DisplayManager.exportList, the following environment
variables are passed:

DISPLAY the associated display name
HOME the initial working directory of the user
LOGNAME the user name
USER the user name
PATH the value of DisplayManager.DISPLAY.systemPath SHELL the value of DisplayManager.DISPLAY.systemShell XAUTHORITY may be set to an authority file

No arguments are passed to the script. Xdm waits until this script exits
before starting the user session. If the exit value of this script is non-zero,
xdm discontinues the session and starts another authentication cycle.

The
sample Xstartup file shown here prevents login while the file /etc/nologin
exists. Thus this is not a complete example, but simply a demonstration
of the available functionality.

The Xsession program is the command which is run as the
user's session. It is run with the permissions of the authorized user.

In
addition to any specified by DisplayManager.exportList, the following environment
variables are passed:

DISPLAY the associated display name
HOME the initial working directory of the user
LOGNAME the user name
USER the user name
PATH the value of DisplayManager.DISPLAY.userPath SHELL the user's default shell (from getpwnam)
XAUTHORITY may be set to a non-standard authority file
KRB5CCNAME may be set to a Kerberos credentials cache name

At most installations, Xsession should look in $HOME for a file .xsession,
which contains commands that each user would like to use as a session. Xsession
should also implement a system default session if no user-specified session
exists. See the section Typical Usage.

An argument may be passed to this
program from the authentication widget using the `set-session-argument' action.
This can be used to select different styles of session. One good use of
this feature is to allow the user to escape from the ordinary session when
it fails. This allows users to repair their own .xsession if it fails, without
requiring administrative intervention. The example following demonstrates
this feature.

This example recognizes the special ``failsafe'' mode, specified
in the translations in the Xresources file, to provide an escape from the
ordinary session. It also requires that the .xsession file be executable
so we don't have to guess what shell it wants to use.

Symmetrical with Xstartup, the Xreset script is run after
the user session has terminated. Run as root, it should contain commands
that undo the effects of commands in Xstartup, removing entries from /etc/utmp
or unmounting directories from file servers. The environment variables
that were passed to Xstartup are also passed to Xreset.

Xdm controls local servers using POSIX signals. SIGHUP
is expected to reset the server, closing all client connections and performing
other cleanup duties. SIGTERM is expected to terminate the server. If these
signals do not perform the expected actions, the resources DisplayManager.DISPLAY.resetSignal
and DisplayManager.DISPLAY.termSignal can specify alternate signals.

To control
remote terminals not using XDMCP, xdm searches the window hierarchy on
the display and uses the protocol request KillClient in an attempt to clean
up the terminal for the next session. This may not actually kill all of
the clients, as only those which have created windows will be noticed.
XDMCP provides a more sure mechanism; when xdm closes its initial connection,
the session is over and the terminal is required to close all other connections.

Xdm responds to two signals: SIGHUP and SIGTERM. When sent
a SIGHUP, xdm rereads the configuration file, the access control file,
and the servers file. For the servers file, it notices if entries have
been added or removed. If a new entry has been added, xdm starts a session
on the associated display. Entries which have been removed are disabled
immediately, meaning that any session in progress will be terminated without
notice and no new session will be started.

When sent a SIGTERM, xdm terminates
all sessions in progress and exits. This can be used when shutting down
the system.

Xdm attempts to mark its various sub-processes for ps(1)
by editing
the command line argument list in place. Because xdm can't allocate additional
space for this task, it is useful to start xdm with a reasonably long command
line (using the full path name should be enough). Each process which is
servicing a display is marked -display.

To add an
additional local display, add a line for it to the Xservers file. (See the
section Local Server Specification.)

Examine the display-specific resources
in xdm-config (e.g., DisplayManager._0.authorize) and consider which of them
should be copied for the new display. The default xdm-config has all the
appropriate lines for displays :0 and :1.

This directs xdm to manage sessions on all three of these terminals. See
the section Controlling Xdm for a description of using signals to enable
and disable these terminals in a manner reminiscent of init(8)
.